Shipping unit converter
Convert parcel weights and dimensions between metric and imperial — with the figure rounded the way a carrier will actually bill it, not just the mathematically exact one.
Weight
Converted
5.291lb
As a carrier bills it
6.00lb
rounded up to the next whole pound
2.400 kg · 5.291 lb. Exact by definition: 1 lb = 0.45359237 kg.
Dimensions
Converted
45.720cm
For a DIM calculation
18in
UPS & FedEx round each side up to the next whole inch
45.720 cm · 18.000 in. Exact by definition: 1 in = 2.54 cm.
Why a shipping-specific converter
Any converter will tell you that 2.4 kg is 5.291 lb. What matters at a shipping counter is that the carrier will bill it as 6 lb, because rounding is always upward and always applied per piece. That single difference is the reason this tool exists rather than a search-engine answer box.
The second reason is unit pairing. Every downstream calculation in shipping — volumetric weight, girth, CBM — is unit-specific, and a converted number dropped into a formula expecting the other system is the most common and most expensive mistake in the whole workflow.
Common shipping conversions
| From | To | Multiply by | Note |
|---|---|---|---|
| Inches | Centimetres | 2.54 | Exact by definition |
| Centimetres | Inches | 0.393701 | Divide by 2.54 |
| Feet | Centimetres | 30.48 | Exact — 12 × 2.54 |
| Pounds | Kilograms | 0.45359237 | Exact by definition |
| Kilograms | Pounds | 2.204623 | Divide by 0.45359237 |
| Ounces | Grams | 28.349523 | Mass ounce, not fluid ounce |
| Grams | Ounces | 0.035274 | 1 lb = 16 oz |
| Cubic metres | Cubic feet | 35.3147 | For CBM and freight quotes |
| Cubic inches | Cubic centimetres | 16.387064 | 2.54³ — not 2.54 |
Conversion constants are exact by international definition and never need updating. Everything else on this site has a review cadence; this table does not.
Where units matter in shipping
- Volumetric divisors. 5,000 is cm³/kg; its imperial equivalent is 139 in³/lb. Mixing them understates volumetric weight by about twelve times. See the volumetric weight calculator, which swaps the divisor automatically with the unit.
- Size limits. Carriers publish combined length-and-girth caps in inches, worldwide. Converting a limit rather than converting your measurement introduces rounding error exactly at the threshold where it decides acceptance — so the girth checker converts your input instead.
- Dimension rounding. UPS and FedEx round each fractional inch up before applying the divisor, so a metric measurement converted to 11.02 in is billed as 12 in. Convert first, then round — never the reverse.
- Customs declarations. State the unit explicitly and use one system throughout. A declaration with metric weight and imperial dimensions is a query waiting to happen.
- Freight quotes. Forwarders switch between CBM and cubic feet freely. One cubic metre is 35.3147 cubic feet — worth knowing by heart if you compare quotes across markets.
Worked example
A metric packing list, an imperial rate card
A supplier lists a carton as 45 × 35 × 28 cm, 4.2 kg. Your US carrier quotes in inches and pounds at a 139 divisor.
45 ÷ 2.54 = 17.72 → 18 in (rounded up)
35 ÷ 2.54 = 13.78 → 14 in
28 ÷ 2.54 = 11.02 → 12 in
18 × 14 × 12 = 3,024 in³ ÷ 139 = 21.8 → 22 lb volumetric
4.2 kg = 9.26 lb actual → billed on 22 lb
Note how much the ceiling rule costs here: 11.02 inches becoming 12 adds nearly two pounds of billable weight on its own. Had the same carton been quoted metric at a 5,000 divisor, it would have come to 44,100 ÷ 5,000 = 8.8 kg — about 19.4 lb. The metric and imperial answers are not meant to match exactly, and the gap is entirely rounding.
Convert once, at the start
Pick the unit system your carrier bills in, convert every input to it before doing anything else, and stay there. Converting intermediate results is where errors compound — particularly with volume, where the conversion factor is cubed.
How we source and maintain this data
The inch (2.54 cm) and the pound (0.45359237 kg) have been exact by international agreement since 1959, so these figures cannot drift and this is the one page on the site with nothing to maintain. What we do add is the shipping layer: carrier rounding behaviour, and the unit-pairing rules that make a correct conversion produce a wrong answer when it lands in the wrong formula.
Review cadence: Never. Conversion constants are exact by international definition. Last reviewed August 2026. This tool is built and maintained by the ParcelTracking team, who run multi-carrier tracking across 3,000+ carriers.
Primary sources
Unit conversion FAQ
1 kg is about 2.205 lb. The exact relationship runs the other way: one pound is defined as exactly 0.45359237 kilograms, so 1 kg = 2.20462262… lb. For a shipping label, 2.205 is close enough; for a customs declaration on a high-value consignment, use the full conversion.
Multiply by 2.54 — the inch is defined as exactly 2.54 cm, so this conversion is not an approximation. Going the other way, divide by 2.54. Convert each dimension separately and only then multiply them together; converting the volume afterwards invites a mistake, since the volume factor is 2.54³ ≈ 16.387, not 2.54.
Because carriers bill in whole or half units. A 2.1 kg parcel is typically charged as 2.5 kg, and a 7.2 lb one as 8 lb. Rounding is always up, never to nearest, and it is applied per piece — which is why splitting a shipment across more boxes than necessary quietly adds billed weight.
Whichever the destination expects, stated consistently, with the unit written out. The failure mode is not choosing wrong — it is a form where the weight is metric and the dimensions imperial, or where the unit is left off entirely. An ambiguous declaration is one of the more common causes of a customs query.
It should not — but pairing a converted number with the wrong divisor absolutely does. Volumetric divisors are unit-specific: 5,000 is cm³ per kg and 139 is in³ per lb. Applying 5,000 to a measurement in inches understates the volumetric weight by roughly twelve times, which is the single most expensive arithmetic mistake in parcel shipping.
An ounce is mass — about 28.35 grams — and a fluid ounce is volume. Shipping always uses the mass ounce. It matters on customs declarations for liquids, where declaring a fluid measure as a weight produces a figure customs cannot reconcile with the parcel on the scale.
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